As computers become more powerful and the techniques of converting photographic images to and from digital form are able to reproduce images of professional photographic quality, there is an increasing need for computer based workstations which are able to interactively perform image editing and image processing operations on such digitized images. However, professional quality images are very large in terms of the amount of digital data and current computer equipment cannot perform even simple computations on such images in a time reasonable for interactive processing.
The prior art contains examples of products which provide a suite of user operations and give interactive performance for some of those operations. Other operations will take a long time (as long as an hour or two) to complete; the operator cannot do any other operations in the meantime.
One such system is disclosed in European Pat. No. EP 0112 414 A1 entitled "Image Transformations on an Interactive Raster Scan or Matrix Display" by R. L. A. Cottrell.
The interactive raster-scanned display device of that patent uses alternative images which are substituted for the full image. An alternate image contains considerably less detail to be drawn and erased than the full image it replaces.
Other known systems edit images by selecting (extracting) a portion of the scene to be operated upon, which portion is then reinserted back into the full scene. See, for example, U.S. Pat. No. 4,189,744, entitled "Apparatus for Generating Signals Representing Operator-Selected Portions of a Scene" by G. Stern, and U.S. Pat. No. 4,746,980, entitled "Video Processing System" by A. C. Petersen.
The present invention is based on the scheme of operating on a large image in sections to minimize the user's wait time for completing selected operations.